Compact mechanical joint balancer

ABSTRACT

The present invention relates to devices and methods for balancing joints, including knee joints. The devices convert unequal forces at a joint to a rotation or displacement of a pointer or gauge. The devices are able to display the relative difference in force between the lateral and medial sides of a joint from flexion to extension. In certain aspects, the devices are useful for balancing the knee during total knee surgery. The devices can be inserted between the trial femoral and tibial components of the knee and measures whether one condyle experiences more force than the other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/621,852, filed Jan. 25, 2018, the contents of which areincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

In the normal intact knee, the relative position between the femur andthe tibia is controlled by the shape of the bearing surfaces and by the4 major ligaments crossing the knee; the anterior and posteriorcruciates and the medial and lateral collaterals. As the knee is flexedand extended, the lengths of the ligaments and the shape of the bearingsurfaces work in harmony to maintain stability, without excessivelooseness or tightness. When the components of a total knee are insertedat surgery, it is important that the components are inserted accurately,and that the geometry of the components is sufficiently close toanatomic, so that the ligaments can still maintain the correct stabilitybetween the femur and the tibia.

In a typical surgical procedure, the bone cuts are made, then the trialcomponents are inserted. At this stage, the knee is flexed and extendedto determine whether the knee comes into extension withouthyperextending, or having an extension lag. The thickness of the tibialcomponent is adjusted if necessary. Then an assessment is made if thebalancing is correct throughout flexion. A simple evaluation method isto remove the trials, introduce a spacer block between the cut surfacesof the femur and tibia with the knee in extension, and move the tibiainto varus and valgus to assess the relative stiffnesses. This isrepeated at 90 degrees flexion. If either the medial or lateral side ofthe knee is too tight, the tight ligaments are released.

Methods other than the spacer blocks can be used. One method is to use adistractor tool which inserts between the joint surfaces and equalexpansion forces are applied separately to the lateral and medialcondyles, equal distraction gaps being an indicator of balancing. Morerecently, an instrumented tibial trial has been introduced, which takesthe place of the tibial trial component, which measures the lateral andmedial contact forces throughout flexion and displays the forces on acomputer screen.

Thus, there is a need in the art for improved mechanical devices andmethods for balancing joints, including knee joints. The presentinvention meets this need.

SUMMARY OF THE INVENTION

The present invention relates to a joint balancer device, comprising: ahandle having a gauge; a lower plate attached to the handle; and anupper plate aligned in parallel with the lower plate by a gap space,wherein the upper plate is displaceable relative to the lower plate;wherein the upper plate is connected by a mechanical link to the gauge,and wherein the mechanical link magnifies displacement of the upperplate such that the gauge displays the magnified displacement.

In one embodiment, the device further comprises: an axle casingextending posteriorly (towards a joint) from the handle and connected ata posterior end to the lower plate, the axle casing further having alumen; an axle rotatably positioned within the lumen of the axle casing,the axle connected at an anterior end (away from a joint) to themechanical link and at a posterior end to the upper plate.

In one embodiment, the mechanical link comprises: a vertical first beampositioned within a hollow interior of the handle and rotatable about apin secured to the interior of the handle, wherein the first beam isattached at a superior end to a pointer of the gauge; and a verticalsecond beam positioned substantially in parallel with the first beam,the second beam being joined at a superior end to the anterior end ofthe axle and attached at an inferior end to an inferior end of the firstbeam. In one embodiment, a clockwise or a counterclockwise rotation ofthe axle moves the inferior end of the first and second beam in a leftor a right direction, respectively, such that the first beam is rotatedabout the pin in a clockwise or a counterclockwise direction,respectively, to shift the pointer of the gauge in a right or leftdirection, respectively.

In one embodiment, the mechanical link comprises: a vertical first beampositioned within a hollow interior of the handle and having a flexibleinferior section pinched between opposing studs attached to the interiorof the handle, the studs acting as a pivot point, wherein the first beamis attached at a superior end to a pointer of the gauge; and a verticalsecond beam positioned substantially in parallel with the first beam,the second beam being joined at a superior end to the anterior end ofthe axle and attached at an inferior end to an inferior end of the firstbeam. In one embodiment, a clockwise or a counterclockwise rotation ofthe axle moves the inferior end of the first and second beam in a leftor a right direction, respectively, such that the flexible inferiorsection of the first beam bends about the opposing studs to shift thepointer of the gauge in a right or left direction, respectively.

In one embodiment, the mechanical link comprises: a horizontal beampositioned within a hollow interior of the handle and rotatable about apin secured to the interior of the handle, wherein the beam comprises anotch at a posterior end and is attached at an anterior end to a pointerof the gauge; and a tab extending in an inferior direction from theanterior end of the axle, the tab being engaged to the notch of thebeam. In one embodiment, a clockwise or a counterclockwise rotation ofthe axle moves the tab and the posterior end of the beam in a left or aright direction, respectively, such that the beam is rotated about thepin to shift the pointer of the gauge in a right or left direction,respectively.

In one embodiment, the mechanical link comprises: a pointer of the gaugerotatable about a pointer axis and a superiorly positioned notch; and atab extending in an inferior direction from the anterior end of theaxle, the tab being engaged to the notch of the pointer. In oneembodiment, a clockwise or a counterclockwise rotation of the axle movesthe tab in a left or a right direction, respectively, such that thepointer of the gauge is rotated about the pointer axis in acounterclockwise or clockwise direction, respectively.

In one embodiment, the mechanical link comprises: a first and a secondelongate beam adjacently positioned within a hollow interior of thehandle, each elongate beam resting on a fulcrum on the interior of thehandle and having an anterior end as a pointer of the gauge; a firstshort beam extending from a posterior end of the first elongate beam ina lateral direction underneath a left side of the upper plate; and asecond short beam extending from a posterior end of the second elongatebeam in a lateral direction underneath a right side of the upper plate.In one embodiment, an inferior displacement of a side of the upper plateinferiorly displaces the respective short beam underneath the side ofthe upper plate, such that the respective connected long beam isactuated about the fulcrum to shift the pointer of the gauge in asuperior direction. In one embodiment, the upper plate comprisesflexible membranes above the first and second short beams.

In one embodiment, the upper plate has an upper surface contoured to fita femur's condyles or a trial femoral component of a total kneereplacement, and the lower plate has a lower surface contoured to fit atibia's condyles or a resected proximal surface of a tibia in a totalknee replacement.

In one embodiment, the upper plate and the lower plate are separated bya substantially parallel distance between about 1 and 5 mm. In oneembodiment, the distance is maintained in a neutral state by one or moresprings positioned between the upper plate and the lower plate, the oneor more springs selected from the group consisting of: coil springs,conical springs, wave springs, and leaf springs. In one embodiment, thegauge includes a scale having at least one of force units, distanceunits, angle degrees, or unitless markings. In one embodiment, thedevice further comprises one or more pressure sensors positioned betweenthe upper plate and the lower plate.

In one embodiment, the device is configured to measure a relativedifference in force between a lateral side and a medial side of a joint.

In another aspect, the present invention relates to a method ofbalancing a joint, comprising the steps of: providing the balancerdevice of the present invention; inserting the balancer device into ajoint in need of balancing such that the upper and lower plates restagainst opposing surfaces of the joint; flexing the joint through atleast part of its full range of motion; recording the magnitudes ofdisplacement between left and right sides of the joint indicated by thegauge throughout the flexing of the joint; removing the balancer devicefrom the joint; modifying the balance of the joint to reduce oreliminate the magnitudes of displacement between left and right sides ofthe joint.

In one embodiment, the joint is a knee joint or an elbow joint. In oneembodiment, the opposing joint surfaces are opposing bone surfaces,opposing implant surfaces, or combinations thereof. In one embodiment,the balance of the joint is modified by trimming the opposing surfaces,raising the opposing surfaces, adjusting a spacer component between theopposing surfaces, or combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of exemplary embodiments of theinvention will be better understood when read in conjunction with theappended drawings. It should be understood, however, that the inventionis not limited to the precise arrangements and instrumentalities of theembodiments shown in the drawings.

FIG. 1 depicts a perspective view of an exemplary balancer device.

FIG. 2A and FIG. 2B depict perspective views of the handle component ofan exemplary balancer device. FIG. 2A depicts the handle alone. FIG. 2Bdepicts a partial cutaway view of the handle.

FIG. 3A and FIG. 3B depict perspective views of the balancer componentof an exemplary balancer device comprising a condyle and a mechanicallinkage. FIG. 3A depicts the balancer component alone. FIG. 3B depicts apartial view of the bottom surface of the balancer component.

FIG. 4A through FIG. 4C depict various views of the balancer componentof an exemplary balancer device as it receives a load. FIG. 4A depicts afrontal view of the balancer plate and handle plate at rest. FIG. 4Bdepicts a frontal view of the balancer plate and handle plate receivinga load on the right condyle. FIG. 4C depicts a perspective view of thebalancer component receiving a load on the right condyle, causing thepointer or gauge to provide a reading to the right.

FIG. 5A through FIG. 5C depict various views of another exemplarybalancer device. FIG. 5A depicts the balancer device near a knee joint.FIG. 5B depicts a partially cutaway view of the underside of thebalancer device. FIG. 5C depicts the balancer component and pointer orgauge in isolation.

FIG. 6 depicts perspective views of another exemplary balancer device.The balancer device (left) includes a handle (middle) and a balancercomponent (right).

FIG. 7 depicts certain views of the balancer device in FIG. 6, includingthe underside of the plate of a condylar component (left), a partialcutaway view of the device under no load (middle), and a partial cutawayview of the device under load (right).

FIG. 8 depicts perspective views of the balancer device in FIG. 6 asseparable components that can be snap fit together. The separablecomponents include a balancer component (far left) and a handlecomponent (middle left) that can be combined to form the balancer device(middle right), and optionally a cap (far right).

FIG. 9 depicts a partial cutaway view (top) and the internal components(bottom) of another exemplary balancer device.

FIG. 10 depicts a perspective view (top), an underside view (middle),and a partial cutaway view (bottom) of another exemplary balancerdevice.

FIG. 11 depicts a perspective view (top) and a proximal view (bottom) ofanother exemplary balancer device.

FIG. 12 is a flowchart depicting an exemplary method of balancing ajoint using a balancer device.

DETAILED DESCRIPTION

The present invention relates to devices and methods for balancingjoints, including knee joints. The devices convert unequal forces at ajoint to a rotation or displacement of a pointer or gauge. The devicesare able to display the relative difference in force between the lateraland medial sides of a joint from flexion to extension. In certainaspects, the devices are useful for balancing the knee during total kneesurgery. The devices can be inserted between the trial femoral andtibial components of the knee and measures whether one condyleexperiences more force than the other.

Definitions

It is to be understood that the figures and descriptions of the presentinvention have been simplified to illustrate elements that are relevantfor a clear understanding of the present invention, while eliminating,for the purpose of clarity, many other elements typically found in theart. Those of ordinary skill in the art may recognize that otherelements and/or steps are desirable and/or required in implementing thepresent invention. However, because such elements and steps are wellknown in the art, and because they do not facilitate a betterunderstanding of the present invention, a discussion of such elementsand steps is not provided herein. The disclosure herein is directed toall such variations and modifications to such elements and methods knownto those skilled in the art.

Unless defined elsewhere, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, exemplary methods andmaterials are described.

As used herein, each of the following terms has the meaning associatedwith it in this section.

The articles “a” and “an” are used herein to refer to one or to morethan one (i.e., to at least one) of the grammatical object of thearticle. By way of example, “an element” means one element or more thanone element.

“About” as used herein when referring to a measurable value such as anamount, a temporal duration, and the like, is meant to encompassvariations of ±20%, ±10%, ±5%, ±1%, and ±0.1% from the specified value,as such variations are appropriate.

The terms “proximal,” “distal,” “anterior,” “posterior,” “medial,”“lateral,” “superior,” and “inferior” are defined by their standardusage indicating a directional term of reference. For example,“proximal” refers to an upper location from a point of reference, while“distal” refers to a lower location from a point of reference. Inanother example, “anterior” refers to the front of a body or structure,while “posterior” refers to the rear of a body or structure. In anotherexample, “medial” refers to the direction towards the midline of a bodyor structure, and “lateral” refers to the direction away from themidline of a body or structure. In some examples, “lateral” or“laterally” may refer to any sideways direction. In another example,“superior” refers to the top of a body or structure, while “inferior”refers to the bottom of a body or structure. It should be understood,however, that the directional term of reference may be interpretedwithin the context of a specific body or structure, such that adirectional term referring to a location in the context of the referencebody or structure may remain consistent as the orientation of the bodyor structure changes.

Throughout this disclosure, various aspects of the invention can bepresented in a range format. It should be understood that thedescription in range format is merely for convenience and brevity andshould not be construed as an inflexible limitation on the scope of theinvention. Accordingly, the description of a range should be consideredto have specifically disclosed all the possible subranges as well asindividual numerical values within that range. For example, descriptionof a range such as from 1 to 6 should be considered to have specificallydisclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numberswithin that range, for example, 1, 2, 2.7, 3, 4, 5, 5.3, 6, and anywhole and partial increments there between. This applies regardless ofthe breadth of the range.

Balancer Device

Referring now to FIG. 1, an exemplary balancer device 10 is depicted.Balancer device 10 has a superior end 12, an inferior end 14, andcomprises a balancer component 40 partially encased within a handlecomponent 20.

Referring now to FIG. 2A and FIG. 2B, handle 20 of an exemplary balancerdevice 10 is depicted in isolation. Handle 20 comprises housing 22, axlecasing 30, and plate 32. Housing 22 comprises a substantially hollowconstruction having a superior end 12 and an inferior end 14. Housing 22comprises a window 24 and a scale 26 positioned near its superior end12. Scale 26 provides a graded measure of any suitable unit adjacent towindow 24. For example, scale 26 can include at least one of forceunits, distance units, angle degrees, or unitless markings. Housing 22further comprises a first tab slot 28 a and a second tab slot 28 bpositioned on the top of its superior end 12. Pin 38, aligned along axis39, is positioned within the hollow interior of housing 22 and projectsfrom the anterior surface of housing 22 in an anterior to posteriordirection.

Axle casing 30 extends posteriorly from housing 22 and connects at itsposterior end to plate 32. Axle casing 30 comprises a lumen extendingfrom the hollow interior of housing 22 (at axle opening 36) to an openend adjacent to plate 32. Plate 32 can have any suitable shape, such asa substantially planar shape sized to fit within a joint space betweentwo connected bones. Plate 32 has an upper surface that interfaces withbalancer 40. In some embodiments, plate 32 has a flat upper surface. Inother embodiments, plate 32 has a curved upper surface. In someembodiments, plate 32 has a flat lower surface. In other embodiments,plate 32 has a contoured periphery or lower surface having the shape ofa joint space, such as the resected proximal surface of a tibia in atotal knee replacement. Plate 32 includes axle slot 34 positionedopposite from the open end of axle casing 30 and aligned with the lumenof axle casing 30.

Referring now to FIG. 3A and FIG. 3B, balancer 40 of an exemplarybalancer device 10 is depicted in isolation viewed from an anteriordirection, alternately called the underside. Balancer 40 comprises firstbeam 42, second beam 50, axle 56, and plate 58. First beam 42 and secondbeam 50 each comprises an elongate shape having a superior end 12 and aninferior end 14. First beam 42 comprises pin bore 44 positioned betweenits superior end 12 and inferior end 14. Pin bore 44 is sized to fitaround pin 38 such that first beam 42 is at least partially rotatableabout pin 38. First beam 42 further comprises pointer or gauge 46positioned near its superior end 12 and first tab 48 a positioned on thetop end of its superior end 12. Pointer or gauge 46 is visible throughwindow 24 adjacent to scale 26, such that the position of pointer orgauge 46 indicates the instant numerical measure as measured by balancerdevice 10. First tab 48 a fits within first tab slot 28 a and limits themovement of first beam 42 to the boundaries of first tab slot 28 a.

First beam 42 is attached to second beam 50 at their inferior ends 14 byextension 54. In some embodiments the inferior half of first beam 42below pin bore 44 is at least partially flexible. A flexible inferiorhalf of first beam 42 below pin bore 44 compensates for the differentcenters of rotation of second beam 50 and first beam 42. The flexibleportion also acts as a spring to center pointer or gauge 46 when no loadis present in device 10. In some embodiments, the attachment between theinferior end of first beam 42 and second beam 50 is a rigid attachment,such as by an adhesive, a welding, or by forming first beam 42 andsecond beam 50 as a single continuous piece. In other embodiments, theattachment between the inferior end of first beam 42 and second beam 50is a separable attachment, such as by slotting the inferior end 14 offirst beam 42 into an opening in extension 54. Second beam 50 is therebypositioned parallel and adjacent to first beam 42, such that both canfit within the hollow interior of housing 22. Second beam 50 comprisesindent 52 between its superior end 12 and inferior end 14. Indent 52provides freedom for second beam 50 to travel around pin bore 44. Secondbeam 50 comprises second tab 48 b positioned on the top end of itssuperior end 12. Second tab 48 b fits within second tab slot 28 b andlimits the movement of second beam 50 to the boundaries of second tabslot 28 b.

Axle 56 extends posteriorly from the superior end 12 of second beam 50along axis 31 and connects at its posterior end to plate 58. Plate 58comprises axle tip 60 positioned opposite from axle 56 and aligned withaxis 31. Plate 58 can have any suitable shape, such as a substantiallyplanar shape sized to fit within a joint space between two connectedbones. In some embodiments, plate 58 has a flat upper surface. In otherembodiments, plate 58 has a contoured upper surface having a shape thatfits in a joint space, such as a shape that fits against the condyles ofa trial femoral component of a total knee replacement. As describedelsewhere herein, the bottom surface of plate 58 is contoured to fit theupper surface of plate 32. For example, a plate 58 having a flat lowersurface fits with a plate 32 having a flat upper surface, and a plate 58having a curved lower surface fits with a plate 32 having a curved uppersurface.

The lower surface of plate 58 has at least two springs 62 positionedopposite from each other to the left and to the right of axle 56.Springs 62 can be any suitable spring, such as a coil spring, a conicalspring, a wave spring, a leaf spring, and the like. The lower surface ofplate 58 is in parallel alignment with the upper surface of plate 32 atrest, with springs 62 maintaining a constant height difference betweenboth plates at rest, as well as restoring parallel alignment to bothplates after displacement of plate 58, thereby functioning as acentering mechanism to zero pointer or gauge 46 of device 10. Plate 58and plate 32 can be separated by any suitable height, such as a heightbetween about 1 and 5 mm. In some embodiments, the height between plate58 and plate 32 is 2.5 mm.

Balancer device 10 uses balancer 40 and handle 20 to provide a readingof the relative difference in force between the lateral and medial sidesof a joint by translating displacement of plate 58 into a proportionalmovement of pointer or gauge 46. The displacement can be an angulardisplacement, a rotation, or a vertical displacement. Referring now toFIG. 4A through FIG. 4C, the operational relationship between balancer40 and handle 20 is depicted. It should be understood that while jointsattached to a body as a point of reference can have medial and lateralsides, for the sake of example a hypothetical joint being measured bybalancer device 10 has a left and a right side as depicted in FIG. 4Band FIG. 4C. In FIG. 4A, balancer device 10 is shown at rest. Plate 58of balancer 40 and plate 32 of handle 20 are held in parallel alignmentby springs 62. In FIG. 4B, an imbalance in a hypothetical joint leads toa relative difference in force that is greater on the right side, whichdepresses right spring 62 on plate 58. In FIG. 4C, the greater force onthe right side of plate 58 causes axle 56 to rotate about axis 31 in aclockwise direction, such as up to 5 degrees or up to 2.5 degrees.Second beam 50, being connected at its superior end to axle 56, pivotsin a clockwise direction about its connection with axle 56, causing itsinferior end to move laterally to the left. The leftward movement of theinferior end of second beam 50 also shifts the inferior end of firstbeam 42 in a leftward direction due to the connection between secondbeam 50 and first beam 42 at extension 54. First beam 42, beingrotatably connected to pin 38, thereby pivots in a clockwise directionabout axis 39, causing the superior end of first beam 42, along withpointer or gauge 46 to move laterally to the right. In variousembodiments, the position of axis 39 can be raised or lowered to adjustthe magnification of movement between the inferior end 14 of second beam50 and pointer or gauge 46.

In summary, a relative difference in force between the left and rightside of a joint exerts a greater load on a respective side of plate 58.The greater load displaces plate 58, such as an angular displacement, arotation, or a vertical displacement, which rotates axle 56. Therotation of axle 56 and the mechanically linked movement of second beam50 and first beam 42 is translated to a shift in the position of pointeror gauge 46 to the left or to the right, whereupon pointer or gauge 46points to a unit on scale 26 of housing 22 to indicate the relativedifference in force in the joint on the side with the greater load.Movement in pointer or gauge 46 is thereby representative of a magnifiedmagnitude of the movement of plate 58.

Referring now to FIG. 5A through FIG. 5C, an exemplary balancer device70 is depicted. Balancer device 70 comprises a housing 72 with asuperior end 12 and an inferior end 14. Housing 72 comprises a window 74near its superior end 12 sized to fit a pointer or gauge 90. Housing 72may further comprise a scale positioned near its superior end 12 thatprovides a graded measure of any suitable unit adjacent to window 74(not pictured). For example, the scale can include at least one of forceunits, distance units, angle degrees, or unitless markings. Axle casing76 extends posteriorly from the superior end 12 of housing 72 andconnects at its posterior end to plate 78. Axle casing 76 comprises alumen extending from housing 72 to an open end adjacent to plate 78.

Plate 78 can have any suitable shape, such as a substantially planarshape sized to fit within a joint space between two connected bones.Plate 78 has an upper surface that interfaces with the lower surface ofplate 82, such that a flat upper surface of plate 78 fits with a flatlower surface of plate 82, and a curved upper surface of plate 78 fitswith a curved lower surface of plate 82. In some embodiments, plate 78has a flat lower surface. In other embodiments, plate 78 has a contouredlower surface having a shape that fits in a joint space, such as a shapethat fits with the condyles of a tibia in a knee joint. Plate 78includes axle slot 80 positioned opposite from the open end of axlecasing 76 and aligned with the lumen of axle casing 76.

Plate 82 rests on the upper surface of plate 78 and is connected to theposterior end of axle 84. Axle 84, aligned along axis 86, extendsanteriorly through the lumen of axle casing 76 into housing 72. Plate 82comprises axle tip 83 positioned opposite from axle 84 and aligned withaxis 86. Plate 82 can have any suitable shape, such as a substantiallyplanar shape sized to fit within a joint space between two connectedbones. In some embodiments, plate 82 has a flat upper surface. In otherembodiments, plate 82 has a contoured upper surface having a shape thatfits in a joint space, such as a shape that fits with the condyles of afemur in a knee joint. The lower surface of plate 82 has at least twosprings 88 positioned opposite from each other to the left and to theright of axle 84. Springs 88 can be any suitable spring, such as a coilspring, a conical spring, a wave spring, a leaf spring, and the like.The lower surface of plate 82 is in parallel alignment with the uppersurface of plate 78 at rest, with springs 88 maintaining a constantheight difference between both plates at rest. Plate 82 and plate 78 canbe separated by any suitable height, such as a height between about 1and 5 mm. In some embodiments, the height between plate 82 and plate 78is 2.5 mm.

Axle 84 comprises tab 85 at its anterior end that seats within notch 94of pointer or gauge 90. Balancer device 70 thereby is able to provide areading of the relative difference in force between the lateral andmedial sides of a joint by translating displacement of plate 82 into aproportional movement of pointer or gauge 90. The displacement can be anangular displacement, a rotation, or a vertical displacement.

While joints attached to a body as a point of reference can have medialand lateral sides, for the sake of describing the function of balancerdevice 70 in an example, a hypothetical joint being measured by balancerdevice 70 has a left and a right side relative to the orientation of thedevice in FIG. 5A and FIG. 5B. An imbalance in a hypothetical jointleads to a relative difference in force that is greater on the rightside, which depresses the right spring 88 of plate 85 and causes axle 84to rotate in a clockwise direction along axis 86, such as up to 5degrees or up to 2.5 degrees. The rotation of axle 84 in a clockwisedirection pivots tab 85 in a clockwise direction to the left, whichpushes notch 94 in the left direction, causing pointer or gauge 90 topivot along axis 92 to the left. In this embodiment, pointer or gauge 90would point to a measure of magnitude, whereupon a user taking care toreverse the orientation may assign the greater load to the correct sideof imbalance (e.g. the pointer or gauge 90 pointing to the leftindicates a greater load on the right side of plate 82). In someembodiments, pointer or gauge 90 points towards inferior end 14,whereupon tab 85 pushing notch 94 in the left direction causes pointeror gauge 90 to pivot along axis 92 to the right, in the same directionas the greater load on the right side of plate 82 (not pictured). Inevery embodiment, movement in pointer or gauge 90 is therebyrepresentative of a magnified magnitude of the movement of plate 82.

Referring now to FIG. 6, an exemplary balancer device 100 is depicted.Balancer device 100 has a superior end 102, an inferior end 104, andcomprises a balancer component 124 partially encased within a handlecomponent 106. Handle 106 comprises housing 108, axle casing 116, andplate 120. Housing 108 comprises a substantially hollow constructionwith a window 110 and a scale 112 positioned near its superior end 102.Scale 112 provides a graded measure of any suitable unit adjacent towindow 110. For example, scale 112 can include at least one of forceunits, distance units, angle degrees, or unitless markings. Housing 108further comprises a first tab slot 114 a and a second tab slot 114 bpositioned on the top of its superior end 102. Visible in FIG. 7 (middleand right), housing 108 further comprises opposing studs 146 having agap space in-between.

Axle casing 116 extends posteriorly from housing 108 and connects at itsposterior end to plate 120. Axle casing 116 comprises a lumen extendingfrom the hollow interior of housing 108 to an open end adjacent to plate120. Plate 120 can have any suitable shape, such as a substantiallyplanar shape sized to fit within a joint space between two connectedbones. Plate 120 has an upper surface that interfaces with balancer 124.In some embodiments, plate 120 has a flat upper surface. In otherembodiments, the upper surface of plate 120 comprises recess 121. Insome embodiments, plate 120 has a flat lower surface. In otherembodiments, plate 120 has a contoured periphery or lower surface havingthe shape of a joint space, such as the resected proximal surface of atibia in a total knee replacement. Plate 120 includes axle slot 122positioned opposite from the open end of axle casing 116 and alignedwith the lumen of axle casing 116.

Balancer 124 comprises first beam 126, second beam 132, axle 138, andplate 140. First beam 126 and second beam 132 each comprises an elongateshape. First beam 126 comprises pointer or gauge 128 and first tab 136 aat superior end 102 and a flexible beam 130 at inferior end 104, whereinfirst tab 136 a is sized to fit within first tab slot 114 a. Flexiblebeam 130, similar to the flexible inferior half of first beam 42,magnifies the movement of pointer or gauge 128 and acts as a spring tocenter pointer or gauge 128 when no load is present in device 100.Pointer or gauge 128 is visible through window 110 adjacent to scale112, such that the position of pointer or gauge 128 indicates theinstant numerical measure as measured by balancer device 100. Flexiblebeam 130 has a width that is smaller than first beam 126, such thatflexible beam 130 fits within the gap space between opposing studs 146in the interior of housing 108 (FIG. 7, middle and right). In someembodiments, studs 146 are positioned from about one third of the heightof handle 106. In various embodiments, the position of studs 146 can beraised or lowered within housing 108 to adjust the magnitude of movementbetween the inferior end 104 of second beam 132 and pointer or gauge128. Second beam 132 comprises second tab 136 b at superior end 102 andextension 134 at inferior end 104, wherein second tab 136 b is sized tofit within second tab slot 114 b. First beam 126 is attached by way offlexible beam 130 to second beam 132 at their inferior ends 104 byextension 134. In some embodiments, the attachment at extension 134 is arigid attachment, such as by an adhesive, a welding, or by forming firstbeam 126 and second beam 132 as a single continuous piece. In otherembodiments, the attachment at extension 134 is a separable attachment,such as by slotting inferior end 104 of flexible beam 130 into anopening in extension 134. Second beam 132 is thereby positioned paralleland adjacent to first beam 126, such that both can fit within the hollowinterior of housing 108.

Axle 138 extends posteriorly from superior end 102 of second beam 132along axis 118 and connects at its posterior end to plate 140. Plate 140comprises axle tip 142 positioned opposite from axle 138 and alignedwith axis 118. Plate 140 can have any suitable shape, such as asubstantially planar shape sized to fit within a joint space between twoconnected bones. In some embodiments, plate 140 has a flat uppersurface. In other embodiments, plate 140 has a contoured upper surfacehaving a shape that fits in a joint space, such as a shape that fitsagainst the condyles of a trial femoral component of a total kneereplacement. As described elsewhere herein, the bottom surface of plate140 is contoured to fit the upper surface of plate 120. For example, aplate 140 having a flat lower surface fits with a plate 120 having aflat upper surface. In some embodiments the lower surface of plate 140can include support 144 shown in FIG. 7 (left) to increase the stiffnessof plate 140 under load; support 144 can fit within a recess 121 in theupper surface of plate 120. Support 144 comprises two downward slopingsurfaces meeting at a middle edge, wherein the height of the edgecombined with the depth of recess 121 define the height of parallelalignment between the lower surface of plate 140 and the upper surfaceof plate 120 at rest. Plate 140 and plate 120 can be separated by anysuitable height, such as a height between about 1 and 5 mm. In someembodiments, the height between plate 140 and plate 120 is 2.5 mm.

Similar to the embodiments described elsewhere herein, balancer device100 uses balancer 124 and handle 106 to provide a reading of therelative difference in force between the lateral and medial sides of ajoint by translating displacement of plate 140 into a proportionalmovement of pointer or gauge 128. The displacement can be an angulardisplacement, a rotation, or a vertical displacement. Referring now toFIG. 7 (middle and right), the operational relationship between balancer124 and handle 106 is depicted. It should be understood that whilejoints attached to a body as a point of reference can have medial andlateral sides, for the sake of example a hypothetical joint beingmeasured by balancer device 100 has a left and a right side as depictedin FIG. 7 (middle and right). In FIG. 7 (middle), balancer device 100 isshown at rest. Plate 140 of balancer 124 and plate 120 of handle 106 areheld in parallel alignment by the edge of support 144 resting at thebottom of recess 121. In FIG. 7 (right), an imbalance in a hypotheticaljoint leads to a relative difference in force that is greater on theright side, which depresses the right side of plate 140. The greaterforce on the right side of plate 140 causes plate 140 to tilt androtates axle 138 about axis 118 in a clockwise direction, such as up to5 degrees or up to 2.5 degrees. Second beam 132, being connected at itssuperior end 102 to axle 138, pivots in a clockwise direction about itsconnection with axle 138, causing its inferior end 104 to move laterallyto the left. The leftward movement of the inferior end 104 of secondbeam 132 also shifts the inferior end of flexible beam 130 in a leftwarddirection due to the connection between second beam 132 and flexiblebeam 130 at extension 134. The movement of flexible beam 130, beingconstrained by studs 146, thereby pivots the superior end 102 of firstbeam 126 in a clockwise direction, causing pointer or gauge 128 to movelaterally to the right. Movement in pointer or gauge 128 is therebyrepresentative of a magnified magnitude of the movement of plate 140.

In some embodiments, handle 106 and balancer 124 can be snap fittogether to assemble balancer device 100, as depicted in FIG. 8. Forexample, extension 134 (FIG. 8, far left) can be sized to have a widthsubstantially equal to flexible beam 130, such that extension 134 andflexible beam 130 can both slide in between the gap space betweenopposing studs 146. Handle 106 (FIG. 8, middle left) can have an axleslot 122, an axle casing 116, and a housing 108 having open superiorends 102, enabling balancer 124 to be inserted into handle 106 from asuperior direction (FIG. 8, middle right). In some embodiments, balancerdevice 100 can further include cap 150 (FIG. 8, far right) to close offthe superior ends 102 of axle casing 116 and housing 108.

Referring now to FIG. 9, an exemplary balancer device 200 is depicted.Balancer device 200 comprises a housing 206 with an anterior end 202 anda posterior end 204. Housing 206 comprises a window 208 at its anteriorend 202 sized to fit a pointer or gauge 232. Housing 206 may furthercomprise a scale 210 positioned at its anterior end 202 that provides agraded measure of any suitable unit adjacent to window 208. For example,the scale can include at least one of force units, distance units, angledegrees, or unitless markings. Axle casing 212 extends posteriorly fromposterior end 204 of housing 206 and connects at its posterior end toplate 216. Axle casing 212 comprises a lumen extending from housing 206to an open end adjacent to plate 216. Plate 216 can have any suitableshape, such as a substantially planar shape sized to fit within a jointspace between two connected bones. Plate 216 has an upper surface thatinterfaces with the lower surface of plate 220, such that a flat uppersurface of plate 216 fits with a flat lower surface of plate 220, and acurved upper surface of plate 216 fits with a curved lower surface ofplate 220. In some embodiments, plate 216 has a flat lower surface. Inother embodiments, plate 216 has a contoured lower surface having ashape that fits in a joint space, such as a shape that fits with thecondyles of a tibia in a knee joint. Plate 216 includes axle slot 218positioned opposite from the open end of axle casing 212 and alignedwith the lumen of axle casing 212.

Plate 220 rests on the upper surface of plate 216 and is connected tothe posterior end of axle 224. Axle 224, aligned along axis 214, extendsanteriorly through the lumen of axle casing 212 into housing 206. Plate220 comprises axle tip 222 positioned opposite from axle 224 and alignedwith axis 214. Plate 220 can have any suitable shape, such as asubstantially planar shape sized to fit within a joint space between twoconnected bones. In some embodiments, plate 220 has a flat uppersurface. In other embodiments, plate 220 has a contoured upper surfacehaving a shape that fits in a joint space, such as a shape that fitswith the condyles of a femur in a knee joint. In some embodiments, thelower surface of plate 220 has springs positioned opposite from eachother to the left and to the right of axle 224. The springs can be anysuitable spring, such as a coil spring, a conical spring, a wave spring,a leaf spring, and the like. In some embodiments, the lower surface ofplate 220 has a support formed by two downward sloping surfaces meetingat a middle edge resting against the top surface of plate 216. Invarious embodiments, the lower surface of plate 220 and the uppersurface of plate 216 are maintained in parallel alignment at rest with agap height in between. Plate 220 and plate 216 can be separated by anysuitable height, such as a height between about 1 and 5 mm. In someembodiments, the height between plate 82 and plate 78 is 2.5 mm.

Balancer device 200 further comprises an elongate beam 228 having notch229 at its posterior end 204 and pointer or gauge 232 positioned at itsanterior end 202. Beam 228 is secured to the interior of housing 206 atpin 230 and is rotatable about pin 230 along pin axis 231. In someembodiments, pin 230 is movable along housing 206 and fits within anelongate slot within beam 228, enabling pin 230 to adjust themagnification of movement between the posterior end 204 of beam 228 andpointer or gauge 232. Axle 224 comprises table 226 at its anterior end202 that seats within notch 229 of beam 228. In some embodiments, beam228 further comprises spacer 234 to maintain the alignment between beam228 and tab 226 of axle 224. Balancer device 200 is thereby able toprovide a reading of the relative difference in force between thelateral and medial sides of a joint by translating displacement of plate220 into a proportional movement of pointer or gauge 232. Thedisplacement can be an angular displacement, a rotation, or a verticaldisplacement.

While joints attached to a body as a point of reference can have medialand lateral sides, for the sake of describing the function of balancerdevice 200 in an example, a hypothetical joint being measured bybalancer device 200 has a left and a right side relative to theorientation of the device in FIG. 9. An imbalance in a hypotheticaljoint leads to a relative difference in force that is greater on theright side, which depresses the right side of plate 220 and causes axle224 to rotate in a clockwise direction along axis 214, such as up to 5degrees or up to 2.5 degrees. The rotation of axle 224 in a clockwisedirection pivots tab 226 in a clockwise direction to the left, whichpushes notch 229 and the posterior end 204 of beam 228 laterally to theleft. Beam 228 rotates about pin axis 231, causing its anterior end 202and pointer or gauge 232 to move laterally to the right. Movement inpointer or gauge 232 is thereby representative of a magnified magnitudeof the movement of plate 220.

Referring now to FIG. 10, an exemplary balancer device 300 is depicted.Balancer device 300 comprises a housing 306 with an anterior end 302 anda posterior end 304. Housing 306 comprises a window 308 at its anteriorend 302 wherein the anterior ends of long beam 318 a and long beam 318 bare visible. Housing 306 may further comprise a scale 310 positioned atits anterior end 302 that provides a graded measure of any suitable unitadjacent to window 308. For example, the scale can include at least oneof force units, distance units, angle degrees, or unitless markings.Housing 306 connects at its posterior end 304 to lower plate 312, upperplate 314 a, and upper plate 314 b. Lower plate 312 can have anysuitable shape, such as a substantially planar shape sized to fit withina joint space between two connected bones. Lower plate 312 can have asubstantially flat lower surface or a contoured lower surface having ashape that fits in a joint space, such as a shape that fits with thecondyles of a tibia in a knee joint. Upper plate 314 a and upper plate314 b can each have any suitable shape, such as a substantially planarshape sized to fit within a joint space between two connected bones. Insome embodiments, upper plate 314 a and upper plate 314 b each has aflat upper surface. In other embodiments, upper plate 314 a and upperplate 314 b each has a contoured upper surface having a shape that fitsin a joint space, such as a shape that fits with the condyles of a femurin a knee joint. Upper plate 314 a and upper plate 314 b arecantilevered over lower plate 312 and are maintained in parallelalignment by gap 316. Gap 316 can have any suitable height, such as aheight between about 1 and 5 mm. In some embodiments, the height betweenplate 82 and plate 78 is 2.5 mm.

Balancer device 300 further comprises long beam 318 a adjacent to longbeam 318 b, each positioned within the hollow interior of housing 306.Long beam 318 a and long beam 318 b each rest on fulcrum 322 positionedon the interior of housing 306. In some embodiments, fulcrum 322 ismovable along housing 306 to adjust the magnification of movementbetween the posterior end 304 and the anterior end 302 of long beam 318a and long beam 318 b. Long beam 318 a and long beam 318 b are eachconnected to short beam 320 a and short beam 320 b, respectively, attheir posterior ends 304. Short beam 320 a and short beam 320 b are eachpositioned underneath upper plate 314 a and upper plate 314 b,respectively. Balancer device 300 is thereby able to provide a readingof the relative amount of force applied on the lateral and medial sidesof a joint by translating displacement of upper plate 314 a and upperplate 314 b into a proportional movement of the anterior ends 302 oflong beam 318 a and long beam 318 b.

While joints attached to a body as a point of reference can have medialand lateral sides, for the sake of describing the function of balancerdevice 300 in an example, a hypothetical joint being measured bybalancer device 300 has a left and a right side relative to theorientation of the device in FIG. 10 (bottom). A hypothetical jointapplies forces to upper plate 314 a and upper plate 314 b (which in thiscase is greater on the right side and lesser on the left side), whichdisplaces upper plate 314 b and short beam 320 b a in a greater inferiordirection than upper plate 314 a and short beam 320 a. The inferiordisplacement of short beam 320 a and short beam 320 b also displaces theposterior ends 304 of long beam 318 a and long beam 318 b in an inferiordirection, respectively, causing the anterior ends 302 of long beam 318a and long beam 318 b to be displaced in a superior direction due tofulcrum 322. The greater inferior displacement of short beam 320 b istranslated to a proportionally greater superior displacement of theanterior end 302 of long beam 318 b, and the lesser inferiordisplacement of short beam 320 a is translated to a proportionallylesser superior displacement of the anterior end 302 of long beam 318 a.Movement in the anterior ends 302 of long beam 318 a and long beam 318 bis thereby representative of a magnified magnitude of the movement ofupper plate 314 a and upper plate 314 b, respectively.

Referring now to FIG. 11, an exemplary balancer device 400 is depicted.Balancer device 400 is similar to balancer device 300 in many respects,including a similar housing 406 having an anterior end 402 and aposterior end 404, a window 408, a scale 410, and long beam 416 a andlong beam 416 b each resting on a fulcrum (not visible) and connected attheir posterior ends 404 to short beams (not visible). Balancer 400further employs a lower plate 412 that is covered by membrane 414.Balancer device 400 functions similarly to balancer device 300, whereindisplacement of the left or right side of membrane 414 corresponds to aninferior displacement of a corresponding short beam and a superiordisplacement of the anterior end 402 of a corresponding long beam 416 aand/or long beam 416 b.

While exemplary balancer devices of the present invention are describedabove, the balancer devices are nonetheless amenable to any suitablemodification to augment their function. In various embodiments, thedimensions of the plates of the balancer devices described elsewhereherein are amenable to adjustment. For example, in certain embodiments,the plates can receive one or more additional spacer plates havingsubstantially similar planar shapes with different heights, such thatthe one or more additional spacer plates can be attached to the uppersurface and lower surfaces of the plates to increase the height of eachplate. In other embodiments, the plates can be removable and replaceablewith plates having different planar shapes or different heights. Invarious embodiments, the one or more additional spacer plates and thereplaceable plates can be used to adjust the contours of the plates toimprove the fit between the balancer devices and a joint of interest. Invarious embodiments, the upper surface of the upper plates are shallow,such that the femoral component of any condylar replacement artificialknee can locate at two separate points.

In various embodiments, the several components of the assorted balancerdevices can be combined and rearranged without altering their functionto accommodate different orientations and configurations. For example,exemplary balancer devices described herein have vertically orientedhandles, but it should be understood that embodiments havinghorizontally oriented handles, handles in line with the axles and axlecasings, and variously angled and dimensioned handles are contemplated.

The components of the balancer devices of the present invention can bemade using any suitable method known in the art. The method of makingmay vary depending on the materials used. For example, componentssubstantially comprising a metal may be milled from a larger block ofmetal or may be cast from molten metal. Likewise, componentssubstantially comprising a plastic or polymer may be milled from alarger block, cast, or injection molded. In some embodiments, thecomponents may be made using 3D printing or other additive manufacturingtechniques commonly used in the art. 3D printing enables the entirety ofthe device to be printed in a single session with a briefpost-processing treatment that removes sacrificial support structuresbetween movable parts. In some embodiments, the materials can withstandcommonly used sterilization techniques, enabling the devices to bereusable. In other embodiments, inexpensive methods permit the devicesto be single-use and disposable.

Method of Use

The present invention also includes methods of using the balancerdevices described herein to balance a joint. Referring now to FIG. 12,an exemplary method 500 of balancing a joint is depicted. Method 500begins with step 502, wherein a balancer device having a handle, agauge, a lower plate, and an upper plate, wherein the upper plate ismechanically linked to the gauge such that the gauge displays amagnitude of displacement of the upper plate is provided. In step 504,the balancer device is inserted into a joint in need of balancing suchthat the upper and lower plates rest against opposing surfaces of thejoint. In step 506, the joint is flexed through at least part of itsfull range of motion. In step 508, the magnitudes of displacementbetween left and right sides of the joint indicated by the gauge arerecorded throughout the flexing of the joint. In step 510, the balanceof the joint is modified to reduce or eliminate the magnitudes ofdisplacement between left and right sides of the joint.

The joint can be any suitable joint, including but not limited to kneejoints and elbow joints. The opposing surfaces of the joint can therebybe opposing bone surfaces of the joint, such as the femoral condyles andthe tibial condyles of the knee. In certain embodiments, the balancerdevices are useful in balancing joint replacements. In some embodiments,the balancer devices are useful in balancing total knee replacements.The opposing surfaces of the joint can thereby be opposing implantsurfaces of the joint replacement, such as the trial femoral condylesand the trial tibial plateau of a replacement knee, as well as anyopposing bone surfaces of the joint that contact the implant surfaces.The balance of the joint can be modified in any suitable manner. Forexample, the opposing surfaces may be trimmed or raised to balance anyrelative differences in force between the left and right sides of thejoint. In certain joint replacements, the joining of the opposingsurfaces can be modified by adjusting a spacer component that fitsbetween the opposing surfaces. The gauge readings indicate whether aforce is greater on the left or the right side of the joint, and themagnitudes of displacement indicate how much greater the force is.

In some embodiments, steps 502 through step 510 are performed in theorder recited. In some embodiments, step 504 through step 508 may berepeated to verify that the modification performed in step 510 correctlybalanced the joint. If the repeated step 508 indicates that themagnitudes of displacement are satisfactorily reduced or eliminated,then the joint is substantially balanced. If the repeated step 508indicates that unsatisfactorily high magnitudes of displacement arestill present, step 510 may be repeated. In some embodiments, step 504through step 510 may be repeated until the magnitudes of displacementare satisfactorily reduced or eliminated.

The disclosures of each and every patent, patent application, andpublication cited herein are hereby incorporated herein by reference intheir entirety. While this invention has been disclosed with referenceto specific embodiments, it is apparent that other embodiments andvariations of this invention may be devised by others skilled in the artwithout departing from the true spirit and scope of the invention. Theappended claims are intended to be construed to include all suchembodiments and equivalent variations.

What is claimed is:
 1. A joint balancer device, comprising: a handlehaving a gauge; a lower plate attached to the handle; and an upper platealigned in parallel with the lower plate by a gap space, wherein theupper plate is displaceable relative to the lower plate; wherein theupper plate is connected by a mechanical link to the gauge, and whereinthe mechanical link magnifies displacement of the upper plate such thatthe gauge displays the magnified displacement.
 2. The device of claim 1,further comprising: an axle casing extending posteriorly (towards ajoint) from the handle and connected at a posterior end to the lowerplate, the axle casing further having a lumen; an axle rotatablypositioned within the lumen of the axle casing, the axle connected at ananterior end (away from a joint) to the mechanical link and at aposterior end to the upper plate.
 3. The device of claim 2, wherein themechanical link comprises: a vertical first beam positioned within ahollow interior of the handle and rotatable about a pin secured to theinterior of the handle, wherein the first beam is attached at a superiorend to a pointer of the gauge; and a vertical second beam positionedsubstantially in parallel with the first beam, the second beam beingjoined at a superior end to the anterior end of the axle and attached atan inferior end to an inferior end of the first beam.
 4. The device ofclaim 3, wherein a clockwise or a counterclockwise rotation of the axlemoves the inferior end of the first and second beam in a left or a rightdirection, respectively, such that the first beam is rotated about thepin in a clockwise or a counterclockwise direction, respectively, toshift the pointer of the gauge in a right or left direction,respectively.
 5. The device of claim 2, wherein the mechanical linkcomprises: a vertical first beam positioned within a hollow interior ofthe handle and having a flexible inferior section pinched betweenopposing studs attached to the interior of the handle, the studs actingas a pivot point, wherein the first beam is attached at a superior endto a pointer of the gauge; and a vertical second beam positionedsubstantially in parallel with the first beam, the second beam beingjoined at a superior end to the anterior end of the axle and attached atan inferior end to an inferior end of the first beam.
 6. The device ofclaim 5, wherein a clockwise or a counterclockwise rotation of the axlemoves the inferior end of the first and second beam in a left or a rightdirection, respectively, such that the flexible inferior section of thefirst beam bends about the opposing studs to shift the pointer of thegauge in a right or left direction, respectively.
 7. The device of claim2, wherein the mechanical link comprises: a horizontal beam positionedwithin a hollow interior of the handle and rotatable about a pin securedto the interior of the handle, wherein the beam comprises a notch at aposterior end and is attached at an anterior end to a pointer of thegauge; and a tab extending in an inferior direction from the anteriorend of the axle, the tab being engaged to the notch of the beam.
 8. Thedevice of claim 7, wherein a clockwise or a counterclockwise rotation ofthe axle moves the tab and the posterior end of the beam in a left or aright direction, respectively, such that the beam is rotated about thepin to shift the pointer of the gauge in a right or left direction,respectively.
 9. The device of claim 2, wherein the mechanical linkcomprises: a pointer of the gauge rotatable about a pointer axis and asuperiorly positioned notch; and a tab extending in an inferiordirection from the anterior end of the axle, the tab being engaged tothe notch of the pointer.
 10. The device of claim 9, wherein a clockwiseor a counterclockwise rotation of the axle moves the tab in a left or aright direction, respectively, such that the pointer of the gauge isrotated about the pointer axis in a counterclockwise or clockwisedirection, respectively.
 11. The device of claim 1, wherein themechanical link comprises: a first and a second elongate beam adjacentlypositioned within a hollow interior of the handle, each elongate beamresting on a fulcrum on the interior of the handle and having ananterior end as a pointer of the gauge; a first short beam extendingfrom a posterior end of the first elongate beam in a lateral directionunderneath a left side of the upper plate; and a second short beamextending from a posterior end of the second elongate beam in a lateraldirection underneath a right side of the upper plate.
 12. The device ofclaim 11, wherein an inferior displacement of a side of the upper plateinferiorly displaces the respective short beam underneath the side ofthe upper plate, such that the respective connected long beam isactuated about the fulcrum to shift the pointer of the gauge in asuperior direction.
 13. The device of claim 12, wherein the upper platecomprises flexible membranes above the first and second short beams. 14.The device of claim 1, wherein the upper plate has an upper surfacecontoured to fit a femur's condyles or a trial femoral component of atotal knee replacement, and the lower plate has a lower surfacecontoured to fit a tibia's condyles or a resected proximal surface of atibia in a total knee replacement.
 15. The device of claim 1, whereinthe upper plate and the lower plate are separated by a substantiallyparallel distance between about 1 and 5 mm.
 16. The device of claim 15,wherein the distance is maintained in a neutral state by one or moresprings positioned between the upper plate and the lower plate, the oneor more springs selected from the group consisting of: coil springs,conical springs, wave springs, and leaf springs.
 17. The device of claim1, wherein the gauge includes a scale having at least one of forceunits, distance units, angle degrees, or unitless markings.
 18. Thedevice of claim 1, wherein the device is configured to measure arelative difference in force between a lateral side and a medial side ofa joint.
 19. A method of balancing a joint, comprising the steps of:providing the balancer device of claim 1; inserting the balancer deviceinto a joint in need of balancing such that the upper and lower platesrest against opposing surfaces of the joint; flexing the joint throughat least part of its full range of motion; recording the magnitudes ofdisplacement between left and right sides of the joint indicated by thegauge throughout the flexing of the joint; removing the balancer devicefrom the joint; modifying the balance of the joint to reduce oreliminate the magnitudes of displacement between left and right sides ofthe joint.
 20. The method of claim 19, wherein the joint is a knee jointor an elbow joint.
 21. The method of claim 19, wherein the opposingjoint surfaces are opposing bone surfaces, opposing implant surfaces, orcombinations thereof.
 22. The method of claim 19, wherein the balance ofthe joint is modified by trimming the opposing surfaces, raising theopposing surfaces, adjusting a spacer component between the opposingsurfaces, or combinations thereof.